Add a read-only option

We don't save any configuration nor items if this is set. This should be
used with care, and hence there's no short option for this.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/args.c

@@ -51,7 +51,8 @@ enum {
   OPT_FMT_RAPT,
   OPT_FMT_EV,
   OPT_FMT_REV,
-  OPT_FMT_TODO
+  OPT_FMT_TODO,
+  OPT_READ_ONLY
 };
 
 /*
@@ -665,6 +666,7 @@ parse_args (int argc, char **argv)
     {"format-event", required_argument, NULL, OPT_FMT_EV},
     {"format-recur-event", required_argument, NULL, OPT_FMT_REV},
     {"format-todo", required_argument, NULL, OPT_FMT_TODO},
+    {"read-only", no_argument, NULL, OPT_READ_ONLY},
     {NULL, no_argument, NULL, 0}
   };
 
@@ -793,6 +795,9 @@ parse_args (int argc, char **argv)
         case OPT_FMT_TODO:
           fmt_todo = optarg;
           break;
+        case OPT_READ_ONLY:
+          read_only = 1;
+          break;
         default:
           usage ();
           usage_try ();